/Engine/Source/Runtime/LiveLinkInterface/Public/LiveLinkLog.h
Write a warning in to the LiveLink log. If the warning occurred more than once for that SubjectKey, a counter will indicate the number of time it did occurred.
template<typename FormatType, typename... ArgsType> static void WarningOnce ( [FName](API\Runtime\Core\UObject\FName) MessageID, const [FLiveLinkSubjectKey](API\Runtime\LiveLinkInterface\FLiveLinkSubjectKey) & SubjectKey, const FormatType & Format, ArgsType... Args )